Waste energetic stockpiles pose an increasing problem for many countries. Millions of tons of material are stockpiled in the world today, including energetics produced as far back as the First and Second World Wars. Much of this waste is toxic and/or hazardous, and runs the risk of contaminating soil or ground water, as well as endangering the safety of personnel. Therefore, a need has existed for safely and efficiently disposing of these materials.
These waste energetic materials may be generated during the normal process of manufacturing energetics. Energetics which do not conform to ballistic, chemical, or physical specifications may be unusable and require disposal. Waste may also be generated during the loading of munitions through equipment wash down procedures. Waste energetics may also be generated through stockpiles becoming unserviceable due to obsolescence or degradation. However, regardless of the reason, the waste energetic materials found in these stockpiles must be disposed of in a safe and environmentally clean manner.
The preferred manner of disposing of waste energetic material today is to burn it. However, unlike many standard fuels or materials which are burned, such as fuel oil, natural gas, or coal, the combustion properties and by-products of energetics present unique problems during the combustion of these materials.
Energetic materials typically have burn rates which are significantly greater than many conventional fuels such as coal, fuel oil, or gas, typically on the order of several magnitudes. For example, cyclotrimethylenetrinitramine (RDX), a commonly used high explosive, has a burn rate, during detonation, of about 20 kilometers/second, while hydrogen, one of the fastest burning conventional fuels, has a burn rate of about 5 meters/second at best.
Due to the high burn rates, most energetics are difficult to burn controllably. They are easily ignitable, and may progress rapidly through burning, deflagration, and detonation. The burn rates of many energetic materials can also be widely varying and unpredictable. Most standard non-energetic fuels burn regressively, that is, the combustion rate decreases with decreasing fuel. Energetic particles may burn at varying combustion rates, including progressively, due to, for example, surface perforations which may increase the surface area of the fuel during combustion. The risk of pressure excursions, or explosions, during combustion may be great with some energetics if not carefully controlled due to their unpredictable and unstable combustion properties.
Most energetics also do not require the addition of oxygen to combust, as oxygen may be present within the structure of the energetic particles. Therefore, unlike many standard carbonaceous fuels, the combustion of energetics is not easily regulated by simply varying the combustion air flow.
Thus, unique dangers exist in burning energetic material which are not present when using many standard non-energetic fuels and materials. Originally, waste energetics were disposed of through open-air burning or open-air detonation. While these practices are simple, relatively safe, and expedient, there is no control over the pollution generated. Also, some concerns are raised due to the exposure of personnel to some of these materials. Finally, open-air burning or detonation does not utilize any of the heating value of these energetic materials.
Another type of disposal for waste energetic material is through incineration. Typically, the energetics are mixed with water to form a slurry, and are then fed into an incinerator, which ignites the energetic material after the water has evaporated. The type of incinerator used is typically a vertical induced draft, a rotary kiln, or a fluidized bed incinerator. One rotary kiln incinerator is described in U.S. Pat. No. 3,949,548, issued to Bolejack, Jr. et al.
Incineration typically requires the use of slurry tanks and mixers in order to properly prepare energetic materials for incineration. Generally, the energetics are mixed with water in a large tank and continuously stirred and pumped in order to keep the energetics in a slurry mixture. Slurry incineration also requires injection at high pressure either by the mixing pump, or by a steam ejector.
In addition, because the burning properties of many energetics are difficult to control and often unpredictable, the above incinerators may be dangerous or unusable with some energetics. After the water in the slurry has evaporated, the energetics are allowed to heat and ignite uncontrollably. This may result in unpredictable ignition points and flashback if too much energetic material is deposited in an incinerator prior to ignition. These incinerators also do not utilize the energy content of the energetics.
Attempts have been made to utilize some of the energy stored in waste energetics during disposal by burning the energetics in a boiler or furnace along with other fuels. The majority of these systems are simply variations on the energetic incinerators, using an energetic/fuel oil slurry in place of an energetic/water slurry. However, these systems require the same tanks and mixing apparatus as energetic incinerators. Certain energetics are often not readily dissolvable in fuel oil and must be continually mixed and pumped in order to keep the slurry composition homogenous. Also, solvents must be added in some cases in order to facilitate the dissolving of the energetics in the slurry. Since different energetics have different properties, special mixtures and ratios must be used in order to provide different types of energetics in these boilers. Thus, these types of cofiring systems require extensive machinery and processing in order to work effectively.
Also, the energetic/fuel oil slurries still require a great deal of fuel oil in order to work properly. Typically, the percentage of energetics is limited to under 30% by weight in the slurry. The remainder will typically be made up of fuel oil, and possibly a solvent. Additional materials are still being expended in order to dispose of the energetics.
Many of the above energetic disposal systems are not capable of adequately controlling the burning of unpredictable, high energy energetics. The likelihood and danger from flashback is aggravated in the case of energetic fuel, since the energetics have such a high burn rate, and can quickly burn back into the fuel delivery system. Also, because many energetics require no additional oxygen, they may burn all of the way back to the fuel storage, resulting in an obvious safety hazard.
One partial solution to this problem is to inject the fuel into the incinerator or boiler at a rate faster than the flame propagation speed. For example, Muller et al., U.S. Pat. No. 3,878,287, uses flow rate to prevent corrosion of the injectors. A high flow rate, however, may produce flame blowout, when the rate of injection extinguishes the flame.
Another concern that is raised in many areas is assuring the complete combustion of any fuels or materials injected into an incinerator or boiler. It is undesirable and dangerous to eject partially-combusted materials from a device which could later ignite or explode. Previously, complete combustion was facilitated by increasing the dwell time of the material in the combustion chamber. For example, as seen in U.K. Patent Application 2,059,031 and Soviet Union Patent Application 996,799, disclose annular restrictions which decrease the diameter of the outlet of the incinerator or boiler. The pressure created by these restrictions typically slows the passage of material through the combustion chamber.
Many of these baffles may allow for reflection or buildup of some fuel immediately upstream of the baffles. For example, in U.K. Patent Application 2,059,031, the surfaces of the baffles are perpendicular to the flow of fuel through the furnace. Material is able to bounce off the baffle and reflect back into the chamber. Also, the eddies formed at the junction of the furnace wall and the baffle allow material to buildup in corners. This built up fuel may ignite and result in explosions.
Jet aircraft engines provide more thorough combustion with baffles which create turbulence in air flow prior to injection of fuel which provides greater mixing of fuel and air and increases the dwell time. However, by their position in the engine, these baffles cannot prevent flashback.
Finally, premature ignition has not been adequately addressed in the prior art. Energetics are typically unstable and easily ignitable. As a result, energetics run the risk of igniting anywhere in the fuel storage and delivery systems before their actual injection into a combustion system. This problem is typically addressed in the energetics field, as discussed above, by mixing the energetics with stable materials such as water or fuel oil. By mixing with additional materials, however, the associated drawbacks discussed above still exist.
Therefore, a need exists in the art for an energetic disposal system which is capable of recovering the energy of energetics in a safe and efficient manner.